Conventionally, wells in oil and gas fields are built up by establishing a wellhead housing and, with a drilling blow out preventer (BOP) adapter valve installed, drilling down to produce the borehole while successively installing concentric casing strings. The casing strings are cemented at their lower ends and sealed with mechanical seal assemblies at their upper ends. In order to convert the cased well for production, a production tubing string is run in through the BOP and a tubing hanger at its upper end is typically landed in the wellhead. Thereafter the drilling BOP is removed and replaced by a Christmas tree having one or more production bores containing valves and extending vertically to respective lateral production fluid outlet ports in the wall of the tree.
The tubing hanger is installed by a hanger running tool and the tool lowers the tubing hanger down the production bore until it lands on top of a stop shoulder. The stop shoulder is created with a decreased inner diameter portion of the housing in which the hanger is landed, which provides a permanent means to stop the lowering of the tubing hanger.
During subsequent operations, the difference in diameter of inner bore created by the permanent stop shoulder may present an inner diameter that can impede the progress of elements that are intended to be lowered past the stop shoulder. In this case, the utilization of the stop shoulder could present and inner diameter less than the inner diameter that would allow an element such as a workover tool to progress downward through the bore. If no stop shoulder were present, such and impedance would not occur and the maximum inner diameter of the production bore would be available to the operator. In addition, the standard amount of housing required between the production bore and a wellhead casing increases proportionally with the inner diameter of the production bore. If no stop shoulder is present, the amount of material can be decreased, per required standards. The absence of a stop shoulder would create “full” production bore, where the inner diameter of the production bore is limited only by the inner wall of the production bore itself.